Many of the trees and shrubs in High Park are still green! By November most native tree leaves have changed colour and fallen, but plenty of non-native trees are still green and photosynthesizing. This “autumn niche” is a huge advantage for the non-native species because they are still able to grow just as the canopy opens up and more sunlight is available. Up to 20% of a tree’s annual carbon gain can come in this slim window of time (Fridley 2012). This longer growing season is one of the many ways that non-native plants are able to out-compete the native species. City of Toronto, High Park Stewards and Nature Centre participants work hard to manage invasive trees while bolstering native plant populations.

The native oaks have turned colour and lost many leaves while the non-native northern catalpas and buckthorn are still vibrant green. Invasive Norway maples have just recently turned yellow, long after the sugar maples dropped their leaves.